The Fine Gold Structure

Of this solid material, more than four-fifths are gold and less than one-fifth is milk protein fibrils. This corresponds to around 20 carat gold.

The nugget is a three-dimensional mesh of gold. The reason of being so light is because it’s mainly composed of pores and the pores contain air. The resultant material is a type of aerogel. And the end product is the lightest form the precious material – lighter than water and close to being as light as air.

The tiny piece if gold is thousand times lighter than its conventional form of alloys yet can hardly be differentiated from conventional gold with the naked eye because the so-called aerogel also boasts same color and metallic sheen. The nugget is light enough to float on the steamy milk froth on top of a cup of cappuccino. The nugget is also malleable, allowing it to be folded into different shapes.

Even when it seems unbelievable: this is a genuine photograph, in which nothing has been faked. The 20 carats gold foam is lighter than milk foam. (Photo: Gustav Nyström and Raffaele Mezzenga / ETH Zurich)

Challenge of the Drying Process

The scientists created the porous material by first heating milk proteins to produce nanometre-fine protein fibres, so-called amyloid fibrils, which they then placed in a solution of gold salt. The protein fibres interlaced themselves into a basic structure along which the gold simultaneously crystallised into small particles. This resulted in a gel-like gold fibre network. A gentle and laborious drying process is opted using carbon dioxide to dry the material because air drying could damage it.

“One of the big challenges was how to dry this fine network without destroying it,”

explains Gustav Nyström, postdoc in Mezzenga’s group and first author of the corresponding study in the journal Advanced Materials.

The Dark-Red Gold

The manufacturing technique also offers scientists numerous possibilities to deliberately influence the properties of gold in a simple manner. By this means, the scientists can influence not only the color but also other optical properties such as absorption and reflection.

” The optical properties of gold depend strongly on the size and shape of the gold particles,”

says Nyström.

“Therefore we can even change the color of the material. When we change the reaction conditions in order that the gold doesn’t crystallize into microparticles but rather smaller nanoparticles, it results in a dark-red gold.”

Potential Execution

The new material could be used in many of the applications where gold is currently being used Applications in watches and jewelry are two of the obvious possibilities. Another application demonstrated by the scientists is chemical catalysis. It can even be used in applications where light is absorbed or reflected.

Gold is one of the most expensive substances on earth. It has widely been used throughout the world for various purposes for millions of years. The completely new gold particles can lead to a revolution in the use of the luxurious material.